Happening so slowly as to appear to be static(adjective)
In a state of dynamic equilibrium(adjective)
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Use "quasistatic" in a sentence
"Such a process of gradual change could be thought of as akin to a quasistatic process, a thermodynamic process in which equilibrium is maintained by performing the process very slowly."
"To reach the equality for a cycle generally requires quasistatic reversible processes."
"It should be noted that a quasistatic reversible path is an idealisation that is reachable only in the limit of infinitely slow processes."